The present invention relates to oxabicyclooctanes of formula I, to the use thereof in liquid-crystalline media and to liquid-crystal and electro-optical display elements containing the liquid-crystalline media according to the invention.
Liquid crystals are used, in particular, as dielectrics in display devices, since the optical properties of such substances can be modified by an applied voltage. Electro-optical devices based on liquid crystals are extremely well known to the person skilled in the art and can be based on various effects. Examples of such devices are cells having dynamic scattering, DAP cells (deformation of aligned phases), guest/host cells, TN structure having a twisted nematic structure, STN cells (supertwisted nematic), SBE cells (superbirefringence effect) and OMI cells (optical mode interference). The most common display devices are based on the Schadt-Helfrich effect and have a twisted nematic structure.
The liquid-crystal materials must have good chemical and thermal stability and good stability to electric fields and electromagnetic radiation. Furthermore, the liquid-crystal materials should have relatively low viscosity and give short response times, low threshold voltages and high contrast in the cells.
Furthermore, they should have a suitable mesophase, for example a nematic or cholesteric mesophase for the abovementioned cells, at conventional operating temperatures, i.e. in the broadest possible range above and below room temperature. Since liquid crystals are generally used in the form of mixtures of a plurality of components, it is important that the components are readily miscible with one another. Further properties, such as the electrical conductivity, the dielectric anisotropy and the optical anisotropy, must satisfy different requirements depending on the cell type and area of application. For example, materials for cells having a twisted nematic structure should have positive dielectric anisotropy and low electrical conductivity.
For example, media of large positive dielectric anisotropy, broad nematic phases, relatively low birefringence, very high resistivity, good UV and temperature stability and low vapor pressure are desired for matrix liquid-crystal displays having integrated non-linear elements for switching individual pixels (MLC displays).
Matrix liquid-crystal displays of this type are known. Examples of non-linear elements which can be used for individual switching of individual pixels are active elements (i.e. transistors). This is then referred to as an xe2x80x9cactive matrixxe2x80x9d, and a differentiation can be made between two types:
1. MOS (metal oxide semiconductor) or other diodes on silicon wafers as substrates.
2. Thin-film transistors (TFTs) on a glass plate as substrate.
Use of single-crystal silicon as the substrate material limits the display size, since even modular assembly of the various part-displays results in problems at the joints.
In the case of the more promising type 2, which is preferred, the electro-optical effect used is usually the TN effect. A differentiation is made between two technologies: TFTs comprising compound semiconductors, such as, for example, CdSe, or TFTs based on polycrystalline or amorphous silicon. Intensive work is being carried out world-wide on the latter technology.
The TFT matrix is applied to the inside of one glass plate of the display, whilst the other glass plate carries the transparent counterelectrode on the inside. Compared with the size of the pixel electrode, the TFT is very small and has virtually no adverse effect on the image. This technology can also be extended to fully color-compatible image displays, where a mosaic of red, green and blue filters is arranged in such a way that each filter element is located opposite a switchable pixel.
The TFT displays usually operate as TN cells with crossed polarizers in transmission and are illuminated from the back.
The term MLC displays here covers any matrix display containing integrated non-linear elements, i.e., in addition to the active matrix, also displays comprising passive elements, such as varistors or diodes (MIM=metal-insulator-metal).
MLC displays of this type are particularly suitable for TV applications (for example pocket TV sets) or for high-information displays for computer applications (laptops) and in automobile or aircraft construction. In addition to problems with respect to the angle dependence of the contrast and the response times, problems arise in MLC displays owing to inadequate resistivity of the liquid-crystal mixture [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay 84, September 1984: A 210-288 Matrix LCD Controlled by Double Stage Diode Rings, p.141 ff, Paris; STROMER, M., Proc. Eurodisplay 84, September 1984: Design of Thin Film Transistors for Matrix Adressing of Television Liquid Crystal Displays, p.145 ff, Paris]. With decreasing resistance, the contrast of an MLC display drops, and the problem of after-image elimination can occur. Since the resistivity of the liquid-crystal mixture generally drops over the life of an MLC display owing to interaction with the internal surfaces of the display, a high (initial) resistance is very important in order to obtain acceptable service lives. In particular in the case of low-voltage mixtures, it was hitherto not possible to achieve very high resistivities. It is furthermore important that the resistivity increases as little as possible with increasing temperature and after heating and/or exposure to UV radiation. Also particularly disadvantageous are the low-temperature properties of the prior art mixtures. It is required that crystallization and/or smectic phases do not occur even at low temperatures, and that the temperature dependence of the viscosity is as low as possible. MLC displays of the prior art thus do not satisfy current requirements.
Besides liquid-crystal displays which use backlighting, i.e. are operated transmissively and optionally transflectivity, there is also interest in reflecting liquid-crystal displays. These reflected liquid-crystal displays use the ambient light for information display. They thus consume significantly less energy than backlit liquid-crystal displays of corresponding size and resolution. As the TN effect is distinguished by very good contrast, such reflective displays can be read even under bright ambient conditions. This is known even about simple, reflective TN displays like those in, for example, wristwatches and pocket calculators. The principle can also be applied, however, to sophisticated, higher-resolution active-matrix-activated displays such as TFT displays for example. Here, as is the case in the generally used transmissive TFT-TN displays, the use of liquid crystals of low birefringence (xcex94n) is necessary in order to achieve low optical retardation (dxc2x7xcex94n). This low optical retardation results in a generally acceptable low angle-of-view dependence of the contrast (cf. DE 30 22 818). In reflective displays, the use of liquid crystals having low birefringence is even more important than in transmissive displays, since in reflective displays the effective layer thickness traversed by the light is approximately twice that of transmissive displays having the same layer thickness.
Advantages of reflective displays compared with transmissive displays include, in addition to the lower power consumption (no backlighting necessary), the greater economy in terms of space, resulting in very small overall depth, and the lessening of the problems caused by temperature gradients owing to differential heating by the backlighting.
There thus continues to be a great demand for MLC displays having very high resistivity at the same time as a broad operating temperature range, short response times even at low temperatures, and low threshold voltage which do not have these disadvantages or only do so to a reduced extent.
In the case of TN (Schadt-Helfrich) cells, media are desired which facilitate the following advantages in the cells:
broadened nematic phase range (in particular down to low temperatures),
switchability at extremely low temperatures (outdoor use, automobile, avionics),
increased stability on exposure to UV radiation (longer life),
low threshold (drive) voltage
low birefringence for improved observation angle range.
The media available from the prior art do not enable these advantages to be achieved while simultaneously retaining the other parameters.
In the case of supertwisted cells (STN), media are desired which enable greater multiplexibility and/or lower threshold voltages and/or broader nematic phase ranges (particularly at low temperatures). To this end, a further broadening of the parameter latitude available (clearing point, smectic-nematic transition or melting point, viscosity, dielectric quantities, elastic quantities) is urgently desired.
None of the previously known series of compounds having a liquid-crystalline mesophase include a single compound which meets all these requirements. Consequently, as a rule, mixtures of from 2 to 35, preferably from 3 to 18, compounds are prepared in order to obtain substances which can be used as liquid-crystalline phases.
It is an object of the invention to provide MLC displays which do not have the abovementioned disadvantages or have them only to a lesser extent, preferably at the same time having very high resistivities and low threshold voltages. In addition, the compounds according to the invention which have a negative dielectric anisotropy are also suitable for VA applications. Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
The substances used hitherto for this purpose always had certain drawbacks, for example inadequate stability with respect to exposure to heat, light or electric fields, disadvantageous mesophases, elastic and/or dielectric properties.
It has now been found that these and other objects can be achieved if compounds and media according to the invention are used in liquid-crystal displays.
In particular, it was found that the oxabicyclooctanes according to the invention are eminently suitable as components of liquid-crystal media. With their aid, stable liquid-crystalline media can be obtained which are particularly suitable for liquid-crystalline displays, such as those described above. The novel compounds are especially distinguished by high thermal stability, which is advantageous for a high xe2x80x9cholding ratioxe2x80x9d, and have advantageous clearing point and birefringence values. The compounds according to the invention are suitable, in particular, for TFT, OCB, VA and IPS applications.
By providing the oxabicyclooctanes according to the invention, the range of liquid-crystalline substances suitable from various application points of views for preparing liquid-crystalline mixtures is quite generally broadened considerably.
The oxabicyclooctanes according to the invention are colorless in the pure state and form liquid-crystalline mesophases in a temperature range favorably situated for electro-optical use. They are chemically-, thermally- and light-stable.
The invention therefore includes oxabicyclooctanes of the general formula I 
in which
L1 and L2 independently of one another, are H or F,
R1 and R2 independently of one another, are CN or halogen or alkyl having from 1 to 12 C atoms which is unsubstituted or mono- to perhalo-substituted by halogen, CN or CF3, it also being possible for one or more CH2 groups to be replaced, in each case independently of one another, by xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94, , (i.e., 1,3-cyclobutylene), xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CFxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94 in such a way that S and/or O atoms are not linked directly to one another,
A1-4 are, independently of one another: trans-1,4-cyclohexylene, in which one or two nonadjacent CH2 groups can be replaced by xe2x80x94Oxe2x80x94 and/or xe2x80x94Sxe2x80x94; 1,4-phenylene, in which one or two CH groups can also be replaced by N; 1,4-cyclohexenylene; 1,4-bicyclo-(2,2,2)-octylene; piperidine-1,4-diyl-; naphthalene-2,6-diyl; decahydro-naphthalene-2,6-diyl; or 1,2,3,4-tetrahydronaphthalene-2,6-diyl; where the above rings can be monosubstituted or polysubstituted by F, Cl, CN, CF3,
Z1 and Z2 each, independently of one another, are xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CF2CF2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)3Oxe2x80x94, xe2x80x94O(CH2)3xe2x80x94, xe2x80x94CF2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CFxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or a single bond,
n1 is 0 or 1,
n2 is 0 or 1, and
n3 is 0, 1 or 2
with the proviso
that n1=0, if n2=0.
The invention also relates to the use of oxabicyclooctanes of formula I as components of liquid-crystalline media.
The invention also relates to a liquid-crystalline medium comprising at least two liquid-crystalline components containing at least one oxabicyclooctane of formula I.
The invention also relates to a liquid-crystal display element, especially an electro-optical display element, which as the dielectric contains a liquid-crystalline medium according to the invention.
If R1 and/or R2 are an alkyl radical and/or an alkoxy radical, this can be straight-chain or branched. It is preferably straight-chain, has 1, 2, 3, 4, 5, 6 or 7 C atoms and therefore preferably means methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, also octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy.
Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5 -, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.
If R1 and/or R2 are an alkyl radical in which a CH2 group has been replaced by xe2x80x94CHxe2x95x90CHxe2x80x94, this can be straight-chain or branched. Preferably it is straight-chain and has from 2 to 10 C atoms. In particular, it is therefore vinyl, prop-1- or prop-2-enyl, but-1-, 2- or but-3-enyl, pent-1-, 2-, 3- or pent-4-enyl, hex-1-, 2-, 3-, 4- or hex-5-enyl, hept-1-, 2-, 3-, 4-, 5- or hept-6-enyl, oct-1-, 2-, 3-, 4-, 5-, 6- or oct-7-enyl, non-1-, 2-, 3-, 4-, 5-, 6-, 7- or non-8-enyl, dec-1-, 2-, 3-, 4-, 5-, 6-, 7-, 8- or dec-9-enyl.
If R1 and/or R2 are an alkyl radical in which one CH2 group has been replaced by xe2x80x94Oxe2x80x94 and by xe2x80x94COxe2x80x94, these are preferably adjacent. They therefore comprise an acyloxy group xe2x80x94COxe2x80x94Oxe2x80x94 or an oxycarbonyl group xe2x80x94Oxe2x80x94COxe2x80x94. Preferably these are straight-chain and have 2 to 6 C atoms. In particular, they therefore are acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxy-ethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonyl methyl, ethoxycarbonyl-methyl, propoxycarbonylmethyl, butoxycarbonyl methyl, 2-(methoxycarbonyl)ethyl, 2-(ethyloxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxy-carbonyl)butyl.
If R1 and/or R2 are an alkyl radical in which one CH2 group has been replaced by unsubstituted or substituted xe2x80x94CHxe2x95x90CHxe2x80x94 and an adjacent CH2xe2x80x94 group has been replaced by CO or COxe2x80x94O or Oxe2x80x94CO, said alkyl radical can be straight-chain or branched. Preferably it is straight-chain and has from 4 to 13 C atoms. In particular, it therefore is acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxy-pentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.
If R1 and/or R2 are an alkyl or alkenyl radical monosubstituted by CN or CF3, said radical is preferably straight-chain. The substitution by CN or CF3 can be in any position.
If R1 and/or R2 are an alkyl or alkenyl radical at least monosubstituted by halogen, said radical is preferably straight-chain, and halogen is preferably F or Cl. In the case of polysubstitution, the halogen is preferably F. These resulting radicals also include perfluorinated radicals. In the case of monosubstitution, the fluorine or chlorine substituent can be in any position, but is preferably in the xcfx89 position.
If one of the rings A1-4 is trans-1,4-cyclohexylene, in which one or two nonadjacent CH2 groups are replaced by O and/or S, the following structures are preferred: 
and their mirror images.
If one of the rings A1-4 is 1,4-phenylene, in which one or two CH groups are replaced by N, the following structures are preferred: 
and their mirror images.
If one of the rings A1-4 is 1,4 phenylene, which is mono or polysubstituted with F, Cl, CN or CF3, the following structures are preferred: 
in which L1-3, independently of one another, are the said substituents, but preferably F.
The cyclohexenylene-1,4-diyl radical preferably has the following structures: 
Preferred compounds of the general formula I are those in which n1=0. Particularly preferred compounds of the general formula I are those in which n2=0, too.
Particularly preferred are oxabicyclooctanes of the general formula (Ia), 
in which 
L1-6 each, independently of one another, are H or F,
Y is F, Cl, CN or an alkyl or alkoxy radical having from 1 to 6 C atoms which is substituted with one or more halogen atoms, in which radical one or more CH2 groups can also be replaced by xe2x80x94Oxe2x80x94 or xe2x80x94CHxe2x95x90CHxe2x80x94, O atoms not being linked directly to one another,
n is 0 or 1.
Here, Y is preferably F, Cl, CN, CF3, CF2H, OCF3, OCF2H, OCFHCF3, OCFHCH2F, OCFHCHF2, OCF2CH3, OCF2CH2F, OCF2CHF2, OCF2CF2CF2H, OCF2CF2CH2F, OCFHCF2CF3, OCFHCF2CHF2, OCFHCFHCF3, OCH2CF2CF3, OCF2CF2CF3, OCF2CFHCHF2, OCF2CH2CHF2, OCFHCF2CHF2, OCFHCFHCHF2, OCFHCH2CF3, OCH2CFHCF3, OCH2CF2CHF2, OCF2CFHCH3, OCF2CH2CHF2, OCFHCF2CH3, OCFHCFHCHF2, OCFHCH2CF3, OCH2CF2CHF2, OCH2CFHCHF2, OCF2CH2CH3, OCFHCFHCH3, OCFHCH2CHF2, OCH2CF2CH3, OCH2CFHCHF2, OCH2CH2CHF2, OCHFCH2CH3, OCH2CFHCH3, OCH2CH2CHF2, OCClFCF3, OCClFCClF2, OCClFCHF2, OCFHCCl2F, OCClFCHF2, OCClFCClF2, OCF2CHCl2, OCF2CHCl2, OCF2CCl2F, OCF2CClFH, OCF2CClF2, OCF2CF2CClF2, OCF2CF2CCl2F, OCClFCF2CF3, OCClFCF2CHF2, OCClFCF2CClF2, OCClFCFHCF3, OCClFCClFCF3, OCCl2CF2CF3, OCClHCF2CF3, OCClFCF2CF3, OCClFCClFCF3, OCF2CClFCHF2, OCF2CF2CCl2F, OCF2CCl2CHF2, OCF2CH2CClF2, OCClFCF2CFH2, OCFHCF2CCl2F, OCClFCFHCHF2, OCClFCClFCF2H, OCFHCFHCClF2, OCClFCH2CF3, OCFHCCl2CF3, OCCl2CFHCF3, OCH2CClFCF3, OCCl2CF2CF2H, OCH2CF2CClF2, OCF2CClFCH3, OCF2CFHCCl2H, OCF2CCl2CFH2, OCF2CH2CCl2F, OCClFCF2CH3, OCFHCF2CCl2H, OCClFCClFCHF2, OCFHCFHCCl2F, OCClFCH2CF3, OCFHCCl2CF3, OCCl2CF2CFH2, OCH2CF2CCl2F, OCCl2CFHCF2H, OCClHCClFCF2H, OCF2CClHCClH2, OCF2CH2CCl2H, OCClFCFHCH3, OCF2CClFCCl2H, OCClFCH2CFH2, OCFHCCl2CFH2, OCCl2CF2CH3, OCH2CF2CCHlH2, OCCl2CFHCFH2, OCH2CClFCFCl2, OCH2CH2CF2H, OCClHCClHCF2H, OCH2CCl2CF2H, OCClFCH2CH3, OCFHCH2CCl2H, OCClHCFHCClH2, OCH2CFHCCl2H, OCCl2CH2CF2H, OCH2CCl2CF2H, CHxe2x95x90CF2, OCHxe2x95x90CF2, CFxe2x95x90CF2, OCFxe2x95x90CF2, CFxe2x95x90CHF, OCFxe2x95x90CHF, CHxe2x95x90CHF, OCHxe2x95x90CHF, in particular F, Cl, CN, CF3, CHF2, OCF3, OCHF2, OCFHCF3, OCFHCHF2, OCFHCHF2, OCF2CH3, OCF2CHF2, OCF2CHF2, OCF2CF2CHF2, OCF2CF2CHF2, OCFHCF2CF3, OCFHCF2CHF2, OCF2CF2CF3, OCF2CF2CClF2, OCClFCF2CF3 or CHxe2x95x90CHF2.
Particularly preferably, Y is F, Cl, CN, OCF3 or OCHF2.
The compounds of the formula Ia generally have a high positive dielectric anisotropy xcex94xcex5 and a very high clearing point.
Particularly preferred, in addition, are oxabicyclooctanes of the general formula Ib, 
in which 
L1-6 each, independently of one another, are H or F,
R1 and R2 have the meanings specified above, and
n is 0 or 1,
with the proviso that at least one of the groups
L3, L4, L5 and L6 is F.
Here, R2 is preferably straight-chain alkyl or oxaalkyl having from 1 to 8 C atoms or alkenyl or oxaalkenyl having from 2 to 7 C atoms.
The compounds of the general formula Ib generally have a negative dielectric anisotropy xcex94xcex5, and a low value for the birefringence xcex94n and a high clearing point.
In the oxabicyclooctanes according to the invention, L1 and L2 preferably have identical meanings, i.e. are either both H or both F.
Particularly preferred oxybicyclooctanes of the general formula Ia are the following compounds: 
R1=C3H7:
xcex94xcex5=15.6; xcex94n=0.147; K 79 N (68.0) I 
R1=C3H7:
xcex94xcex5=19.6; xcex94n=0.099; K 161 I 
R1=C3H7:
xcex94xcex5=21.8; xcex94n=0.099 
R1=C3H7:
xcex94xcex5=14.7; xcex94n=0.107
R1=CH3:
xcex94xcex5=23.2; xcex94n=0.160
R1=C5H11:
xcex94xcex5=26.9; xcex94n=0.131
Particularly preferred oxabicyclooctanes of the general formula Ib are the following compounds: 
R1=C3H7:
xcex94xcex5=xe2x88x926.3; xcex94n=0.090 
R1=C5H11:
xcex94xcex5=xe2x88x925.4; xcex94n=0.150 
R1=C3H7:
xcex94xcex5=xe2x88x921.0; xcex94n=0.140
R1=C3H7:
xcex94xcex5=xe2x88x926.0; xcex94n=0.143
The oxabicyclooctanes according to the invention can be prepared, for example, in accordance with the following reaction scheme: 
Prior to carrying out the boronic acid coupling, a hydrogenation of the aromatic ring can be performed.
The liquid-crystalline media according to the invention preferably, in addition to one or more oxabicyclooctanes according to the invention, comprise from 2 to 40, particularly from 4 to 30 components as further constituents. Most especially preferably, these media, in addition to one or more oxabicyclooctanes according to the invention, comprise from 7 to 25 components. These further constituents are preferably selected from nematic or nematogenic (monotropic or isotropic) substances, especially substances from the classes of the biphenyls, terphenyls, phenyl benzoates or cyclohexyl benzoates, phenyl or cyclohexyl esters of cyclohexanecarboxylic acid, phenyl or cyclohexyl esters of cyclohexylcyclohexanecarbonic acid, cyclohexylphenyl ester of benzoic acid, of cyclohexanecarbonic acid or cyclohexylcyclohexanecarbonic acid, phenylcyclohexanes, cyclohexylbiphenyls, phenylcyclohexylcyclobenzenes, 4,4xe2x80x2-biscyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl- or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- or cyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes, 1-phenyl-2-cyclohexylethanes, 1-cyclohexyl-2(4-phenyl-cyclohexyl)ethanes, 1-cyclohexyl-2-biphenylethanes, 1-phenyl-2-cyclohexylphenylethanes and tolanes. The 1,4-phenylene groups in these compounds can also be fluorinated.
The most important compounds potentially suitable as additional constituents of media according to the invention can be characterized by the formulae II, III, IV, V and VI:
Rxe2x80x2xe2x80x94Lxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x83II
Rxe2x80x2xe2x80x94Lxe2x80x94COOxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x83III
Rxe2x80x2xe2x80x94Lxe2x80x94OOCxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x83IV
Rxe2x80x2xe2x80x94Lxe2x80x94CH2CH2xe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x83V
Rxe2x80x2xe2x80x94Lxe2x80x94Cxe2x89xa1Cxe2x80x94Exe2x80x94Rxe2x80x3xe2x80x83xe2x80x83VI
L and E, which can be identical or different, in the formulae II, III, IV, V and VI, each, independently of one another, are a bivalent radical from the group formed by -Phe-, -Cyc-, -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -Pyr-, -Dio-, -G-Phe- and -G-Cyc- and mirror images thereof, where Phe is 1,4-phenylene which is unsubstituted or substituted by fluorine, Cyc is trans-1,4-cyclohexylene or 1,4-cyclohexenylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl, Dio is 1,3-dioxane-2,5-diyl and G is 2-(trans-1,4-cyclohexyl)-ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.
Preferably, one of the radicals L and E is Cyc, Phe or Pyr. E is preferably Cyc, Phe or Phe-Cyc. Preferably, the media according to the invention comprise one or more compounds selected from the compounds of the formulae II, III, IV, V and VI, in which L and E are selected from the group consisting of Cyc, Phe and Pyr, and at the same time one or more components selected from the compounds of the formulae II, III, IV, V and VI in which one of the radicals L and E is selected from the group consisting of Cyc, Phe and Pyr, and the other radical is selected from the group consisting of -Phe-Phe-, -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-, and optionally one or more components selected from the compounds of the formulae II, III, IV, V and VI, in which the radicals L and E are selected from the group consisting of -Phe-Cyc-, -Cyc-Cyc-, -G-Phe- and -G-Cyc-.
In the compounds of the subformulae IIa, IIIa, IVa, Va and VIa, Rxe2x80x2 and Rxe2x80x3 each, independently of one another, are alkyl, alkenyl, alkoxy, alkenyloxy or alkanoyloxy having 1 to 8 carbon atoms. In most of these compounds, Rxe2x80x2 and Rxe2x80x3 differ from one another, one of these radicals usually being alkyl or alkenyl. In the compounds of the subformulae IIb, IIIb, IVb, Vb and VIb, Rxe2x80x3 is xe2x80x94CNxe2x80x94, xe2x80x94CF3, xe2x80x94OCF3, xe2x80x94OCHF2, xe2x80x94F, xe2x80x94Cl or xe2x80x94NCS; Rxe2x80x2 here has the meanings specified for the compounds of subformulae IIa and VIa and is preferably alkyl or alkenyl. Particularly preferably, Rxe2x80x3 is selected from the group consisting of xe2x80x94F, xe2x80x94Cl, xe2x80x94CF3, xe2x80x94OCHF2 and xe2x80x94OCF3. Other variants of the designated substituents in the compounds of the formulae II, III, IV, V and VI are also commonly used, however. Many substances or alternatively mixtures can be obtained in accordance with methods known from the literature or in analogous ways.
The media according to the invention, in addition to components from the group consisting of the compounds IIa, IIIa, IVa, Va and VIa (group 1) also comprise components from the group consisting of the compounds IIb, IIb, IVb, Vb and VIb (group 2), whose proportions are preferably as follows:
Group 1: from 20 to 90%, in particular from 30 to 90%,
Group 2: from 10 to 80%, in particular from 10 to 50%,
the sum of the proportions of the compounds according to the invention and of the compounds from groups 1 and 2 being up to, 100%.
The media according to the invention preferably comprise from 1 to 40%, especially preferably from 5 to 30% of compounds according to the invention, for example, the oxabicyclooctanes of formula I. Also preferred are media comprising more than 40%, in particular from 45 to 90%, of compounds according to the invention. The media preferably comprise from one to five compounds according to the invention.
The preparation of the liquid-crystalline mixtures which can be used according to the invention is effected in a manner customary per se. Generally, the desired quantity of the components used in smaller amounts is dissolved in the components making up the principal constituent, expediently at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again after thorough mixing, for example by distillation. It is also possible to prepare the mixtures in other conventional ways, for example by using premixtures, for example homolog mixtures, or using so-called xe2x80x9cmulti-bottlexe2x80x9d systems.
The dielectrics may also comprise further additives known to those skilled in the art and described in the literature. For example, from 0 to 15 wt %, preferably from 0 to 10 wt %, of pleochroic dyes and/or chiral dopants can be added. The additives are each employed in concentrations of from 0.01 to 6 wt %, preferably from 0.1 to 3 wt %. However, the concentration data for the other constituents of the liquid-crystal mixtures, i.e. of the liquid-crystalline or mesogenic compounds, are given without taking into account the concentrations of these additives.
In the present application and in the examples below, the structures of the liquid-crystal compounds are indicated by means of acronyms, the transformation into chemical formulae being effected in accordance with tables A and B below. All the radicals CnH2n+1 and CmH2m+1 are straight-chain alkyl radicals having n and m C atoms, respectively. n and m are integers, preferably 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12, with the options of n=m or nxe2x89xa0m. The coding in table B is self-evident. In table A, only the acronym for the parent structure is given. In individual cases, the acronym for the parent structure is followed, separated by a hyphen, by a code for the substituents R1, R2, L1 and L2:
Preferred mixture components are shown in tables A and B, where R1, R2, L1 and L2 can have the meanings specified in the table above.
The entire disclosure of all applications, patents and publications, cited above and below, and of corresponding German Application No. 10148485.2, filed Oct. 1, 2001, is hereby incorporated by reference.